The present invention relates to a method and system for detecting characteristics of an optical lens used to read and write information on an information recording medium of an optical disk system, such as DVDs (Digital Versatile Disks), or an optical lens used to form a light spot by focusing light in laser beam machines, laser microscopes or the like, and further relates to a method and system for adjusting the optical lens. The invention also relates to method and system for adjusting an optical unit, for example, method and system for adjusting an optical unit which reads and writes information on an information recording medium of the optical disk system.
In order to read information from a high-density information recording medium of the optical disk system and to store information into this high-density information recording medium, an optical system capable of directing light emitted from a light source correctly to a target place is necessary. Therefore, in particular, the objective lens of an optical system is not only required to have strict optical characteristics for itself, but also has to be fixed to a target place with good precision.
Thus, as a method for inspecting or adjusting an objective lens, it would be conceivable to take a method (jitter method) including the steps of, as shown in FIG. 1, directing a light beam (e.g., laser beam) 2 emitted via an objective lens 1 to a reference object 3 (e.g., optical disk) for use of lens inspection, detecting reflected light from this reference object 3, comparing a read signal 4 resulting from the detection with a reference signal 5, and then adjusting the tilt or the like of the objective lens 1 so that a phase difference 6 between the read signal 4 and the reference signal 5 is minimized or the phase difference falls within a specified allowance value.
However, in general, characteristics of the objective lens 1 vary among individual objective lenses, and there is no definite relation between the degree of tilt or the like of the objective lens 1 and the phase difference 6. Moreover, as shown in FIG. 2, one objective lens 1A and another objective lens 1B, in some cases, show considerably different characteristics (lens tilt angle phase difference characteristics). Also, it is necessary to repeat the comparison between tilt adjustment of the objective lens and signals, and it is difficult to make an objective decision as to which stage the adjustment should be completed. Further, since the read signal 4 includes characteristics unique to the circuit for obtaining this read signal 4, the tilt or the like of the objective lens 1 could not necessarily be grasped enough from the read signal 4.
As a method substituting for the jitter method, it has been discussed to take a method (light intensity measuring method) including steps of, as shown in FIG. 3, condensing light 12 transmitted by an objective lens 11 to an image pickup device (CCD) 14 via a magnifying optical system 13 including a lens, a mirror and the like, displaying a beam spot (see FIGS. 4A, 4B) captured by this image pickup device 14 onto a signal processor 15 or the like, observing the light intensity (density variation pattern) (see FIG. 4A) of the beam spot displayed on the signal processor 15, and thereby inspecting or adjusting the tilt or the like of the objective lens 11. It is noted that FIG. 4A shows a beam spot 16 appearing on the signal processor 15 prior to adjustment with a density variation pattern 17 formed thereabout, while FIG. 4B shows a beam spot 18 appearing on the signal processor 15 after the adjustment without any density variation pattern.
However, this light intensity measuring method is based on light intensity information alone to detect tilt or the like of the objective lens 11, and thus is incapable of fine adjustment, for example, adjustment of the wavelength level of the light 12. Also, since the sensitivity characteristics of the image pickup device 14 vary among places, detection results may differ depending on which part of the image pickup device 14 receives the light 12. Besides, focal shifts of the beam spot 18 would have quite a large effect on the detection result. Furthermore, because of the use of the magnifying optical system 13, adjusting the tilt angle of the objective lens 11 would cause the beam spot 18 to go out of the image pickup device 14, giving rise to a case where the result of the adjustment could not be evaluated. Also, since light intensity of the beam spot 16 is read by human vision, differences among individuals are likely to affect the inspection results.
Accordingly, an object of the present invention is to provide a new lens evaluation method, lens evaluation system, lens adjustment system, and lens adjustment method to substitute for the aforementioned jitter method and light intensity measuring method.
Another object of the present invention is to provide an optical unit adjustment method and system capable of carrying out the adjustment of an optical unit in short time.
Still another object of the present invention is to provide a lens evaluation method and lens evaluation system capable of correctly measuring spherical aberration and defocus without being affected by lens"" local deformation.